Field of the Invention
The present invention relates to an optical scanner and an image forming device incorporating the same.
Description of the Related Art
It is known to form a latent image on a photoconductor as a latent image bearer by deflecting and scanning light in accordance with image information and develop the latent image to create an image. An optical scanner deflects light for scanning and comprises a light source as a laser diode (LD), an optical element as a cylindrical lens to adjust a shape of light from the light source, and a polygon mirror to rotate to deflect the adjusted light for scanning. Prior to writing an image on the photoconductor, the optical scanner controls light to be incident on the polygon mirror and a synchronous sensor in order to acquire write start timing. Then, it starts turning on the light for writing an image on the basis of a synchronous detection signal generated by the synchronous detector.
Japanese Laid-open Patent Application Publication No. 2014-13329 discloses an optical scanner comprising a cylindrical lens having an optical power along a rotational axis (hereinafter, sub scanning direction) of a polygon mirror. The cylindrical lens is cantilevered. Specifically, one end of the cylindrical lens in a main scanning direction orthogonal to both of the optical axis and the sub scanning direction is secured by adhesion on a fixed wall parallel to the main scanning direction.
An optical housing accommodating the light source, optical elements and a polygon scanner is thermally expanded because of heat emission from high-speed rotation of a polygon mirror of the polygon scanner. Due to the thermal expansion, the fixed wall may be tilted, changing the posture of the cylindrical lens accordingly. Along with a postural change, the position at which light is incident on the cylindrical lens is varied in the sub scanning direction. Since the cylindrical lens exerts optical power in the sub scanning direction, the exit position of light from the cylindrical lens changes in the sub scanning direction.
With no tilt of a light receiving surface of the synchronous sensor in the sub scanning direction, the synchronous sensor can detect the light to start writing at proper timing irrespective of a change in the light exit position from the cylindrical lens. However, the light-receiving surface of the synchronous sensor may be tilted relative to the sub scanning direction because of a manufacturing error in a mount on which a unit including the synchronous sensor is disposed or an assembly error in the unit and the mount. In this case, along with the change of light emitted from the cylindrical lens in the sub scanning direction, the synchronous sensor cannot detect the light at the correct timing for synchronous detection. As a result, write start timing is shifted from the right timing so that it is not able to form an image on a desired position of a paper.